1. Field of the Invention
The field of the invention disclosed herein is directed to afocal lens assemblies, and more specifically to afocal lens assemblies used with a collimator having up to a 15 degree field-of-view output for testing an infrared detector assembly.
2. Description of Related Prior Art
In the prior art, thermal imaging systems were developed to overcome distinct disadvantages of other detection methods such as radar or visible optics. These other methods generally operate in an "active" mode in which electromagnetic radiation is emitted and a sensor detects that return signature but allows for detection and countermeasures to render such systems ineffective. Also such active systems are limited due to such performance characteristics as range and day/night operation. First generation Forward Looking Infrared (FLIR) sensors were developed to extend vision beyond the visible light spectrum and are capable of "passive" operation. Such systems allow for superb action since most objects radiate in the IR region. The testing of such systems typically employs collimating optics (usually mirrors) which provide a plane-wave input, and a detector which is positioned in the focal plane of the test system. A more thorough description of system performance testing for first generation FLIRs may be found in Chapter 11 of "Thermal Imaging Systems" by J. M. Lloyd.
Deficiencies in the first generation FLIRs have led to the development of a second generation of FLIRs. First generation FLIRs included deficiencies such as cryogenic cooling and scanning. The second generation of FLIRs were developed to include some of the following characteristics:
1. detector material responsive to ambient temp; PA0 2. the elimination or minimization of cooling "noise"; PA0 3. more efficient cooling technique; PA0 4. staring focal plane arrays which eliminate scanning; PA0 5. simplified power supply PA0 6. up to a 60 degree field-of-view.
With the development of second generation FLIRs there is now a need to measure and test the performance of these systems.